1. Field of the Invention
This invention relates to a suspension system for a vehicle and, more particularly, to a suspension system which can enhance running safety, cornering safety and riding comfort by optimally controlling the change of a camber in accordance with a vehicle's travelling conditions.
2. Description of the Conventional Art
In general, a suspension system for a vehicle connects an axle shaft and a vehicle body to each other and absorbs an impact and vibration from a road surface to increase riding comfort and running safety. To absorb the impact from the road surface, a connection of upper and lower parts of the suspension system should be flexible, and to cape with driving and breaking forces applied to a wheel and centrifugal force in vehicle's turning, a connection in the horizontal direction of the suspension system should be durable.
The suspension system is structurally characterized as either an integral shaft suspension or an independent suspension. The suspension of this invention concerns an independent suspension. There are MacPherson strut type and Wishbone type suspension systems in the independent suspension.
The MacPherson strut type suspension system comprises a strut assembly 105, shock absorbing means, consisting of a shock absorber 101 and a spring 102 and having a lower end fixed to a wheel carrier 103 pivotally supporting a wheel 100 and an upper end supporting a vehicle body 104; and a lower control arm 106 connecting a lower side of the wheel carrier 103 to a lower side of the vehicle body 104, as shown in FIG. 9A.
The range of a wheel's up-and-down movement is determined by the lower control arm 106 during a wheel's up-and-down vibration. The vibration is absorbed by an elastic bushing of a vehicle body-side connecting portion. Impact from a road surface is absorbed by the shock absorber 101 and spring 102 of the strut assembly 105.
However, considering operation steps of the above described suspension system, when the wheel 100 vibrates upward and downward in accordance with traveling conditions, the wheel 100 moves upward and downward in a state where the length of the lower control arm 106 is predetermined. Thus, the wheel 100 moves upward and downward according to a tracing movement M which is formed by the length of lower control arm 106. A camber angle is changed according to the wheel's up-and-down movement and has a great effect on ride comfort, cornering safety, and running stability.
That is, since the wheel side end connecting portion of the lower arm 106 is designed to be disposed at a lower side of the wheel center, when the wheel moves along the tracing movement M, in a normal ascending section, the lower side of the wheel is pushed outward along a curvature of the tracing movement M, and the camber is changed to negative(-). However, in a section over the normal ascending section, the lower control arm 106 ascends and pulls the lower side of the wheel, whereby the camber is changed again to positive(+)(see broken line of FIG. 4A).
The change of the camber as described above is illustrated the broken line of FIG. 4A which will be described in the detailed description of the invention. Further a tread is changed as illustrated in the broken line of FIG. 4B by the change of the camber. Such changes of the camber and tread adversely effect the steering safety and the straight traveling safety of a vehicle.
The Wishbone type suspension system can be classified in two types, a short and long arm type(SLA) and a parallelogram type. The parallelogram type suspension system, as shown in FIG. 9B, is a type such that an upper control arm 111 is the same height as that of a lower control arm 112. This type has a problem that when the wheel 113 moves upward and downward, since each point connected with a wheel carrier 114 of the upper and lower control arms moves in parallel to each other as shown in a broken line, the camber is not changed but the tread is severely changed.
Further, the short and long arms type suspension system, as shown in FIG. 9C, is a type that a lower control arm 122 is longer than an upper control arm 121. This type has a problem that when the wheel 123 moves upward and downward, since the upper control arm 121 has a small curvature tracing movement and the lower control arm 122 has a large curvature tracing movement, the tread is not changed but the camber is severely changed.